Saint Stephen is recognized as the first christian martyr (I would have thought this was Jesus, but I would be wrong). He was born a Jew, preached largely among Jews & died at the hands of Jews. It was Saint Stephen who first blamed the Jews for the death of Jesus. (ACTS7).
But it was not this that brought Wenceslas to Saint Stephen's Day; Stephen's 'day job' was the care & oversight of the poor. When he had free time, he wrangled with the scholars of the varied temples, explaining how they had been chosen by G*d, but he was fed up with them (G*d & Stephen both, fed up with the Jews, that is).
While he reigned, Wenceslas was in negotiation with everyone, inside the realm & out. When modern historians talk about the Balkans being at war for one thousand years, they are talking about a war that dates to the time of Wenceslas & before. He made deals wherever he could; whether he would have honored them is a different question. He was struck down in the doorway of the church in which he sought sanctuary.